The present invention relates to a method and apparatus for the manufacture of miniature structures. In particular, this invention directs itself to pulse-position synchronization for use in Direct Write processes.
Still further, the present invention relates to a method for pulse-position synchronization in which a target is initially exposed to a first pulse of energy. Subsequently a pause in the target exposure exists during which time the relative position between the target and the energy source is adjusted which permits a pause time for positioning the next area of the target which is to be exposed. Once positioning of the target has been achieved, the target is exposed to a second pulse of energy.
Additionally, the present invention relates to a technique for pulse-position synchronization in a fabrication tool which includes a target, a source of energy, a substrate, and control unit operatively coupled to the source of energy as well as the target and the substrate. The fabrication tool is operated in patterned xe2x80x9cadditivexe2x80x9d and patterned xe2x80x9csubtractivexe2x80x9d modes of operation. In the xe2x80x9cadditivexe2x80x9d mode of operation, the target is a material carrier element which has a deposition layer where predetermined areas are ablated in a patterned manner by pulses of energy generated by the source of energy (laser) under the control of a control unit. The depositable material from the deposition layer of the material carrier element is then deposited on a substrate within predetermined deposition regions corresponding to the ablated areas of the deposition layer. The control unit synchronizes the relative motion of the target, substrate and the source of energy in order to (1) expose fresh areas of the target to the laser pulse, (2) provide uniformity of the material deposition on the substrate, and (3) optimize the motion patterns. Thus, miniature structures in the nature of semiconductor chips, electrical and mechanical-electrical elements may be manufactured.
With respect to the xe2x80x9csubtractivexe2x80x9d mode of operation, the material carrier element is removed from the laser path, whereby the substrate is exposed to pulses of energy ablating the surface of the substrate in patterned manner for cleaning or trimming the substrate as well as for creating vias, channels, guides, through holes, etc.
Miniature structures are becoming more widely used as technology advances and a plethora of electrical systems are used in miniaturization of common industrial and domestic appliances. Such structures may be found in TV sets, radios, vehicles, kitchen appliances, computers, etc. Due to the advantage of the use of miniature structures in such electrical systems, a large emphasis has been placed on the development of a wide variety of different manufacturing technologies for fabrication of miniaturized components.
Among others, a Direct Write technology has been developed and successfully applied which uses a laser beam for ablating a source of depositable material. The ablated depositable material from the source is then transferred and deposited at predetermined areas of a workpiece to create miniature structures thereon.
Additionally, a laser micromachining process has been developed which uses a laser beam to ablate predetermined areas of a workpiece to a predetermined depth in order to form vias, through holes, or miniature recesses. This type of process is also applicable to etching, trimming, or cleaning of the workpiece.
In both the Direct Write processes and the laser micromachining processes, coordination of motion between all elements of the system is important. Thus, coordination and control of substrate motion, laser beam scanning, or combinatorial relative motion thereof is of vital importance in the manufacturing process. Specifically, if laser power is maintained in a constant xe2x80x9conxe2x80x9d mode during acceleration or deceleration of the relative motion of the substrate and the laser beam, a non-constant dose of a depositable material is delivered to the substrate. This interferes with deposition processes, resulting in locally varying thickness of the fabricated miniature structures.
Still further, the relative motion between the laser and the substrate must be conducted at a speed of relative motion, since excessive laser dwell may overheat and damage sensitive components already existing on the substrate. In the case of laser micromachining processes, variation of the depth of ablation may result which is unsatisfactory for applications where smooth structures with constant thickness or depth are required for optimum performance.
Commercial systems exist which address the problem of variations in laser exposure due to acceleration or deceleration of relative motion between the substrate and the laser beam. For example, the control unit (Aerotech PC-PSO Personal Computer Add-On board) monitors multi-axis motion and produces position synchronized electrical pulses capable of firing a laser at precise increments of travel. The interval can be software selectable for dynamic control of the deposition process or micromachining process. This control unit typically produces one pulse every time the relative position of the substrate changes by m microns, where m is a number that can be set in the software program that is used in conjunction with the control unit to control the substrate motion. When motion occurs in 2 or 3 dimensions, the control unit is normally capable of carrying out the necessary vector algebra to compute the linear change in position.
If the pulse produced by the control unit every n microns is used to trigger the pulsed laser, the separation between successive laser pulses on the substrate will be constant and variations in exposure of illuminated areas will be eliminated. This approach to control the laser firing is normally called pulse-position synchronization. Since all of the processes in the controller and laser needed to fire the laser pulse occur in microseconds, there is no need to slow or stop the relative motion to achieve position-synchronized pulsing of the laser.
As an example, the system may provide generation of laser pulses each 0.25 micrometer of travel in any direction. Such commercially available systems permit bit mapping laser pulses by clocking-out trigger pulses in accordance with a predetermined pattern while scanning the laser or changing a substrate position where an analogous technique is used in laser printer technology.
Although pulse-position synchronization is routinely used in laser micromachining to remove material, it has not previously been applied to the forward transfer technique for material deposition. Without pulse-position synchronization the number of forward transfer events per unit of displacement varies as the substrate accelerates and decelerates, resulting in thickness variations of the deposited material.
Further, failure to provide precise coordination of the relative motion of the target and the laser beam with activation-deactivation of the laser radiation in conventional systems may cause the ablation of unintended areas of a target, or alternatively deposition of a depositable material on unaimed or unwanted regions. In these cases, the laser pulse may impinge not only onto an area of interest but also onto neighboring regions, thus deteriorating the quality and performance of manufactured miniature structures.
Still further in such conventional systems during the Direct Write processes, successive laser pulses impinge at the source of the depositable material (target ribbon) at areas which may be not close enough to each other which results in inefficient use of the depositable material. If the laser pulses impinge onto already ablated area of the source of the depositable material, the depositable material is not delivered to a required area on the substrate which reduces the yield of high quality miniature structures.
Another disadvantage results from impingement of the laser beam on previously ablated areas of the source of a depositable material which causes unwanted direct access of the laser beam to the surface of the substrate. This may have the effect of destroying structures located on the surfaces of the substrate.
Due to the aforementioned reasons, it is clear that the target ribbon must exhibit motion relative to the focused laser beam, since a xe2x80x9cfreshxe2x80x9d area of the target ribbon must be exposed to each laser pulse. Therefore, a need exists in miniature structures manufacturing industry for pulse-position synchronization techniques applicable to forward transfer processes which are free of disadvantages of the devices and systems of the prior art.
It is therefore an object of the present invention to provide a method and apparatus for pulse-position synchronization in miniature structure manufacturing processes in which precise coordination between the relative motion of the elements of the fabrication tool and activation or deactivation of the source of energy is achieved.
It is a further object of the present invention to provide a method of pulse-position synchronization in direct write technology which permits the material carrier element to be advanced between laser pulses to an unexposed spot adjacent to an already ablated area to permit ablation by a next laser pulse. This provides efficient utilization of the depositable material of the deposition layer mounted or located on the material carrier element.
It is another object of the present invention to provide a method for pulse-position synchronization which includes exposing a target to a first pulse of energy. A pause in the exposure is provided while relative motion at a maximum speed between the target and the energy source is introduced. The relative motion speed between the target and the energy source is reduced or terminated while exposing the target to a second pulse of energy.
It is still a further object of the present invention to provide a method for pulse-position synchronization in a fabrication tool capable of operating in both patterned xe2x80x9cadditivexe2x80x9d and xe2x80x9csubtractivexe2x80x9d modes of operation. With respect to the xe2x80x9cadditivexe2x80x9d mode of operation, pulses of energy impinge onto a material carrier element (a.k.a. target ribbon) to ablate a deposition layer for transferring a depositable material of the deposition layer onto a substrate. In a xe2x80x9csubtractivexe2x80x9d mode of operation pulses of energy impinge onto a substrate for micromachining the surface of the substrate according to a desired pattern.
In accordance with the present invention a method for pulse position synchronization in miniature structures manufacturing processes is carried out in a fabrication tool capable of operating in a patterned xe2x80x9cadditivexe2x80x9d and xe2x80x9csubtractivexe2x80x9d modes. The fabrication tool includes a substrate, a material carrier element, a source of energy capable of generating pulses of energy and a control unit operatively coupled to the source of energy and the target.
In the xe2x80x9cadditivexe2x80x9d mode of operation, the deposition layer formed on the material carrier element is ablated within predetermined areas upon exposure to pulses of energy in order that the ablated depositable material advances or is transferred from the deposition layer to a substrate for deposition.
Alternatively in the xe2x80x9csubtractivexe2x80x9d, i.e., micromachining, mode of operation, the material carrier element is removed from the laser beam path, and the substrate is ablated at predetermined areas upon exposure to pulses of energy for creating various vias, waveguides, channels, or other patterned recesses.
In both modes of operation pulse-position synchronization is carried out by and within the fabrication tool by:
generating a first pulse of energy from a source of energy,
exposing a predetermined area of the target (which is the material carrier element in the xe2x80x9cadditivexe2x80x9d mode of operation, or the substrate in the xe2x80x9csubtractivexe2x80x9d mode of operation) to the first pulse of energy,
terminating the first pulse of energy,
initiating relative motion between the target and the source of energy,
slowing or terminating relative motion speed between the target and the source of energy,
generating a second pulse of energy, and
exposing the target (in an area discrete from the first area) to the second pulse of energy.
In the time period defined by the sequential pulses of energy, the relative motion between the target and the source of energy is driven at relatively high speed. While being exposed to pulses of energy, the relative motion between the target and the source of energy is slowed to less than 10% of the predetermined maximum speed or alternatively the relative motion is terminated.
In the xe2x80x9cadditivexe2x80x9d mode of operation, it is important that the second pulse impinges onto: (a) a non-ablated area of the deposition layer; and (b) a non-ablated area adjacent to that area already ablated by the first pulse of energy. In this manner, a fresh area of the deposition layer is used for each laser pulse, and efficient utilization of the material of the deposition layer is achieved.
To achieve this, the speed of the target ribbon relative to the laser must be at least as high as the speed of the substrate relative to the laser. This may be accomplished in several ways: (a) by attaching the ribbon to the substrate (contact transfer), (b) by moving the target ribbon at a constant speed that exceeds the maximum speed of the substrate, or (c) by programming the control unit to adjust the speed of the ribbon so that it tracks the speed of the substrate.
The target ribbon and substrate may travel in different directions during material deposition. Additionally, the target ribbon and substrate motions may trace out different patterns. For example, the target ribbon may be arranged in a reel-to-reel configuration, such as that used in a movie projector and the substrate may trace out a complicated two-dimensional pattern. With regard to the motion of the target, the key issue is that its motion be such that a fresh area is presented to each laser pulse. It is not necessary that the motion of the target be closely synchronized to the firing of the laser, although synchronization schemes are preferred that would result in more efficient utilization of the target.
The forward transfer deposition system of the present invention permits the capability of material removal, which is gained by removing the target ribbon from the laser path and focusing the laser directly on the substrate thus performing a xe2x80x9csubtractingxe2x80x9d mode of operation.
By applying the pulse-position synchronization technique in conjunction with optimized motion patterns, uniformity of deposition may be improved and variations in thickness minimized.
The source of energy may be a laser generating a laser beam, sources of electron beams or ion beams. If the source of energy is a laser, an ultraviolet laser is preferably used. Where a UV laser is used, the material carrier element is made transparent to the ultraviolet radiation to permit the laser beam to impinge directly onto the deposition layer through the material carrier element.
The present invention is further directed to a device which monitors the motion of the ribbon target, substrate, and source of energy to produce an output pattern of electrical pulses capable of driving a source of energy to generate pulses of energy or to suppress the same. These electrical pulses are delivered at a rate (or interval) that is a function of the relative position between the target ribbon, substrate, and the source of energy.
These and other novel features and advantages of this invention will be fully understood from the following detailed Description of the Accompanying Drawings.